1. Field of the Invention
This invention relates to a gas detector for detecting the presence of a particular gas such as a combustible gas and a hazardous gas beyond a certain level and a method for manufacturing the same. In particular, the present invention relates to a low power gas detector of the semiconductor type suited for use as a gas leak alarm for detecting the presence of excessive amount of gas such as LP gas and commercial or utility gas and giving a warning signal upon detection. More specifically, the present invention relates to a method for manufacturing a metal oxide thin film which may be advantageously used as a gas detecting element in a semiconductor type gas detector or a transparent electrode film in a display panel or photoelectric sensor.
2. Description of the Prior Art
A gas detector using a metal oxide semiconductor such as SnO.sub.2 and ZnO is well known. In such a prior art gas detector, electrodes and/or coil-shaped electrodes also serving as heater coils are provided as buried in the body of metal oxide semiconductor, wherein changes in the resistance of the metal oxide semiconductor due to absorption of a particular gas at the surface are used to detect the presence or overamount of a particular gas. However, one of the paramount disadvantages in the prior art gas detector has been the large power requirement. For example, none of the prior art gas detectors has been suited for use with batteries. Thus, there has been a need for developing a low power gas detector which may be driven by batteries for an extended period of time.
As a gas detecting element of a semiconductor type gas detector, use has been commonly made of a sintered metal oxide semiconductor. As described in the Japanese Patent Laid-open Publication No. 58-30648, the typical method for manufacturing such a gas detecting element is to produce tin oxide by processing tin with dense nitric acid and then a sediment of tin oxide thus obtained is sintered using a binder such as SiO.sub.2 and Al.sub.2 O.sub.3. However, as described above, instead of the prior art gas detector driven by a commercial line voltage, research has been and still is being carried out to develop a battery-driven gas detector. Under the circumstances, it is required to develop a gas detector smaller in scale and thus lower in power consumption. In such a miniaturized gas detector, a gas detecting element as thin as a few microns and as small in area as some hundreds of microns squared must be fabricated. None of the prior art techniques is capable of fabricating such a small-sized gas detecting element.